[Stooky Bill]

Yes… targeting everyone usually means appealing to nobody. 

Yes, the first thing you're taught is 'know your audience' 

The age ranges for the BBC stations mainly exist to prevent them infringing on their rivals, commercial stations have always had to stick to to a particular format or audience as a part of their license. Although they can be quite broad - Radio 2's has no maximum age. The other thing they do is prevent the sort of situation Radio 1 once found itself in whereby the supposed young station was attracting a big audience, but also a lot of old people. Radio 1 on a Saturday when I was a teenager was DLT playing 70s guitar based album tracks and pub games followed by vintage comedy clips and then AOR. Awful. 

But of course commercial radio has its own age ranges too, much tighter than those given to the BBC stations. They have to sell advertising to those groups.